Device for Thermal Control of Recirculated Gases in an Internal Combustion Engine

ABSTRACT

The invention relates to a device for thermal control of recirculated gases in an internal combustion engine, comprising a liquid coolant circuit ( 1 ), connected to an internal combustion engine ( 2 ). The circuit ( 1 ) comprises first thermal coolant/air heat exchanger means ( 3 ), such as a radiator, arranged in a first loop ( 13 ), connected to the engine ( 2 ), second thermal coolant/recirculated exhaust gas heat exchanger means ( 4 ) arranged in a second loop ( 14 ), connected in parallel to the first loop ( 13 ), in order to permit the supply of the second thermal heat exchanger means ( 4 ) with coolant from the first thermal heat exchanger means ( 3 ), characterized in that the ends of the second loop ( 14 ) are directly connected to the body of the first thermal exchanger means ( 3 ).

The invention relates to a device for thermal control of recirculated gases of an internal combustion engine.

In order to increase the efficiency of the recirculation of a portion of the exhaust gases into the fresh intake gases of an engine, with a view at reducing in particular emissions of NOx gases, a heat exchange is usually provided between these recirculated exhaust gases and the liquid coolant of the engine. To this effect, a recycled gases/coolant heat exchanger is supplied with coolant from the exit of the engine by a branch pipe on the water outlet assembly of the engine, upstream of the thermostat.

However, these known systems are not satisfactory in certain operating situations of the engine, as the temperature of the recirculated exhaust gases is not well controlled. In particular, when the temperature of the engine increases, the coolant reaches high temperatures detrimental to the efficiency of the exhaust gases recycling for reducing nitrogen oxides.

FIG. 1 illustrates a device for thermal control of recirculated gases of an internal combustion engine according to the prior art, comprising a circuit 1 of coolant connected to an internal combustion engine 2, the circuit comprising first coolant/air A heat exchanger means A, such as a radiator, arranged in a first loop 13 connected to the engine 2, second coolant/recirculated exhaust gas GB heat exchanger means 4 arranged in a second loop 14 connected in parallel to the first loop 13, to enable supplying the second heat exchanger means 4 with coolant from the first heat exchanger means 3.

Such a construction, conform to the preamble of the main claim, is described in particular in the document FR2752440A1.

The flow rate of the coolant allowed to circulate in the first loop 13 is controlled, for example, by a thermostat 7 arranged in the water outlet assembly 16.

However, in this type of hydraulic construction using a radiator, there is a risk that the fluid flow rate will fluctuate among its components.

Indeed, when the thermostat 7 is completely open to let the coolant circulate in the first loop (arrow 23 on FIG. 1), an parasitic inversion (arrow 24 on FIG. 1) of the circulation direction of fluid can occur in a portion 14 of the circuit 1.

A first pump 10, for example, a mechanical pump, linked to the engine 2, performs the activation of the fluid flow rate in the cooling circuit 1. At high engine speeds, it can happen that a portion of the fluid exiting the engine 2 in the area of the thermostat 7 enters directly into the second exchanger 4 (coolant/recirculated gases exchanger) instead of passing first quasi-exclusively through the radiator 3. This flow rate inversion occurs even when a second pump 5 arranged in the loop 14 of the second exchanger 4 operates in a direction opposed to this inversion.

For a given circuit, when the engine speed is in the order of 3300 rev/min, for example, the mechanical pump 10 of the engine generates a flow rate in the radiator 3 in the order, for example, of 8000 l/hr. In these conditions, a conventional radiator causes a pressure drop in the order of 300 mbar.

When the flow rate is zero, an electrical pump 5 of standard type ensures a counter-pressure in the second loop of about 200 mbar, i.e., lower than the pressure drop in the radiator 3.

As a result, in some operating conditions, there is an inversion of the circulation direction of the fluid in the second exchanger 4 (this parasitic circulation direction is shown by the arrows 24 on FIG. 1). This circulation inversion is preceded by an operating point during which the flow rate is zero or quasi-zero in the second exchanger 4. This zero-flow rate operating point can occur, for example, at an engine speed in the order of 2700 rev/min.

This type of defective operation causes a drop in the efficiency of the radiator and of the second exchanger 4. In case of a zero or low flow rate in the second exchanger 4, there is, in addition, a risk that the coolant will boil in this second exchanger 4.

Further, these degraded operating points can coincide with states of the engine or of other parts in which the thermal control is crucial. Accordingly, it is necessary, on the one hand, to detect the flow rate of fluid circulating in the second exchanger 4, and on the other hand, to provide a complex control strategy for the pump 5.

To solve these problems, one solution consists in providing a check valve 17 in the second branch 14, so as to reduce the flow rate in this branch in a cooling phase of the engine (see FIG. 1). This solution is generally satisfactory for the inverted parasitic flow rate, but it causes a high cost increase in the context of mass production. In addition, the use of a check valve generates an additional pressure drop in the hydraulic circuit and requires the calibration of a leak to maintain a minimum flow rate in the exchanger 4.

Another solution consists in increasing the power of the electrical pump 5 arranged in the second loop 14. This solution has the same drawbacks in terms of costs, requires a complex control strategy for the pump 5, and triggers excess fuel consumption.

An objective of the present invention is to remedy all or part of the drawbacks of the prior art mentioned above.

To this effect, the device for thermal control of recirculated gases of an internal combustion engine according to the invention, otherwise conform to the generic definition given in the preamble above, is characterized essentially in that the ends of the second loop are directly connected to the body of the first heat exchanger means.

Further, the invention can have one or several of the following characteristics:

-   -   the ends of the second loop are connected to an inlet and an         outlet, respectively, of the first heat exchanger means distinct         from the inlet and outlet connecting the first heat exchanger         means to the engine,     -   the ends of the second loop are connected to the first heat         exchanger means so as to connect the inlet and outlet of the         second heat exchanger means with an outlet and an inlet,         respectively, of the first heat exchanger means,     -   the first heat exchanger means comprise at least one heat         exchanger core connected to a fluid inlet assembly and a fluid         outlet assembly, the ends of the second loop being directly         connected to the fluid inlet and outlet assemblies,         respectively,     -   the second loop comprises controlled means for activating the         coolant flow rate, such as a pump,     -   the device comprises means for controlling the coolant flow rate         allowed to circulate in the first loop,     -   the means for controlling the flow rate comprise a valve of the         proportional type, such as a thermostat,     -   the means for controlling the flow rate comprise a pump,     -   the means for activating the flow rate in the second loop and         the means for controlling the flow rate in the first loop are         independent, so as to enable starting or stopping the means for         activating the flow rate in the second loop whatever the flow         rate of coolant allowed to circulate in the first loop.

Other specificities and advantages will appear by reading the following description, made in reference to the Figures in which:

FIG. 1 is a schematic view of a cooling circuit of an internal combustion engine according to the prior art,

FIG. 2 is a schematic view of a cooling circuit of an internal combustion engine according to an exemplary embodiment of the invention,

FIG. 3 is a schematic front view of a detail of FIG. 2, illustrating an exemplary embodiment of the heat exchanger means such as a radiator, in accordance with the invention,

FIG. 4 is a schematic cross-section view along line AA of the heat exchanger means of FIG. 3,

FIG. 5 is a schematic view of a graph illustrating comparative coolant fluid flow rates in the second loop 14 of the circuit as a function of the engine speed.

In addition to the characteristics described above, the device for thermal control according to the prior art shown on FIG. 1 also comprises an optional third loop 19 connected in parallel to the first 13 and second 14 loops of the circuit 1. The third loop 19 comprises a coolant/air exchanger 18 such as an air heater intended, for example, to yield calories to a volume such as a passenger compartment of a vehicle.

Such an internal combustion engine 2 comprises, in a standard manner, intake conduits (not shown) supplying fresh gases to the cylinders of the engine 2. The burned gases GB generated by the combustion in the cylinders are collected by the exhaust conduits (not shown). In a standard manner, a derivation makes it possible to recirculate a portion of the exhaust gases into the intake. To this effect, the derivation can comprise a valve controlled so as to regulate the flow rate of the recirculated gases.

The device according to the invention will now be describe by reference to FIG. 2. For concision purposes, the elements identical to those described above are designated by the same reference numerals and will not be described in details a second time.

The circuit 1 according to the invention is different from that described previously in that the second loop 14 which contains the coolant/recirculated exhaust gases GB exchanger 4 is connected in parallel to the first loop 13 directly to the body of the first heat exchanger means 3. Further, this second loop 14 can operate without check valve 17, and in this case, it includes only a pump 5, preferably an electrical pump.

According to the invention, a very high reduction of the pressure drops at the ends of the second loop 14 is observed, as compared to the solutions of the prior art.

For example, the two ends of the second loop 14 are directly connected to the radiator 3, so as to connect the inlet 11 and outlet 12 of the coolant/recirculated exhaust gases exchanger 4 to an outlet 6 and an inlet 5, respectively, of the radiator 3.

The radiator 3 can comprise a heat exchanger comprising at least one tube/fins core 7 whose ends are connected to a fluid inlet assembly 8 and a fluid outlet assembly 9, respectively (FIGS. 3 and 4). The two ends of the conduits of the second loop 14 can be directly connected to the fluid inlet assembly 8 and fluid outlet assembly 9, respectively, of the radiator 3.

Thus, the invention makes it possible to minimize the hydraulic pressure drops at the terminals of the circuit 14, in particular within the fluid inlet 8 and outlet 9 assemblies, as compared to the system according to the prior art in which the second loop 14 is connected to the conduits or hoses of the first loop 13.

Thus, the invention makes it possible, for a same type of pump 5 arranged in the second loop 14, to postpone the risky operating points (zero or inverted flow rate in the second loop 14 of the coolant/recirculated exhaust gases exchanger) until higher engine speeds. The device according to the invention even makes it possible, in some cases, to eliminate these risky operating modes. The use of a check valve on the second loop 14 can thus be avoided.

FIG. 5 illustrates on a same graph the variation of the flow rate D of coolant in the coolant/recirculated exhaust gases exchanger 4 in liters by minute (in ordinates) as a function of the engine speed N in revolutions per minute (in abscissa). The graph represents this flow rate for a circuit according to the prior art (curve 20) and for a circuit modified in accordance with the invention (curve 21).

This is to say that, for a hydraulic circuit according to the prior art (conform to FIG. 1), it is observed that the flow rate in the second loop 14, and thus in the coolant/recirculated gases exchanger 4, becomes zero and is inverted beginning at about 2700 rev/min.

In contrast, for an identical circuit where only the connection of the second loop 14 has been modified according to the invention (branch pipe directly onto the radiator 3 in accordance with FIG. 2), the flow rate D in the second loop 14 remains above about 8 liters per minute.

The invention enables an optimal thermal control (cooling) of the engine while avoiding the risk that the fluid would boil in the coolant/recirculated exhaust gases exchanger 4 and the risk that the efficiency of this exchanger 4 would become degraded.

As shown on FIGS. 3 and 4, the ends of the second loop 14 can be connected to an inlet 5 and an outlet 6, respectively, of the radiator 3, which are distinct of the inlet 15 and outlet 16 for connecting the radiator 3 to the engine 2.

In particular, the device according to the invention makes it possible to ensure, with a simple and inexpensive structure, an optimal temperature of the recirculated exhaust gases.

In addition, the flow rate increase in the exchanger 3 generated by the pump 5 makes it possible to obtain an increase in efficiency of this exchanger for cooling the engine.

The nominal efficiency of the coolant/recirculated exhaust gases exchanger 4 is maintained over a very large operating range of the engine (including the usage points currently defined in this exchanger). In particular, the invention makes it possible to ensure a minimum flow rate of 5 to 6 l/min in a standard exchanger 4 when this exchanger must be operational.

According to other specificities, the circulations of the coolant in the first 13 and second 14 loop can be controlled independently from each other. The circulation of the coolant in the third loop 19 is also independent form the circulation in the other loop 14.

When the engine 2 is very hot, the circuit 1 according to the invention makes it possible to supply the coolant/recirculated exhaust gases exchanger 4 with coolant cooled by the radiator 3.

When the thermostat 7 controlling the natural circulation of the coolant in the radiator 3 is closed, the coolant circulating in the coolant/recirculated exhaust gases exchanger 4 remains at a temperature close to the ambient temperature. This way, the efficiency of the exchanger 4 is improved, which promotes the reduction of the pollutants in the exhaust gases of the engine (in particular NOx).

The electrical pump 5 of the second circuit 4 can be started to increase the heat exchange between the coolant and the recirculated exhaust gases.

The stopping of this electrical pump 5 also makes it possible to eliminate the circulation of coolant in the coolant/recirculated gases exchanger 4 in the starting phase of the engine, i.e., at a time when the start of a catalysis system has not yet been triggered (in general when the temperature of the exhaust gases is lower than a threshold temperature comprised between 100 and 250° C., in general about 150° C.). This arrangement makes it possible to reduce the pollutants, in particular of the CO and HC type, and thus, it makes it possible to eliminate the standard by-pass on the coolant or on the exhaust gases.

Means for measuring the temperature of the exhaust gases, such as a sensor, can be provided to this effect in the area of the exhaust.

In the same way, if the circuit 14 comprises a check valve, when the recirculation of the exhaust gases is interrupted by the corresponding valve, the pump 5 arranged in the second loop 14 is not started. Preferably, the pump 5 is stopped with a determined delay after the recycling is stopped. Thus, preferably, the pump 5 arranged in the second loop 14 is supplied only when the exhaust gases are recirculated and their temperature has reached a threshold value (catalyst started).

When the operating mode of the engine requires simultaneous cooling of the engine 2 and of the recirculated exhaust gases, the thermostat 7 is opened and the pump 5 arranged in the second loop 14 is started. The coolant cooled in the radiator 3 is divided between the engine 2 and the coolant/recirculated exhaust gases exchanger 4. Similarly, the radiator 3 is supplied by a mixture of liquid from the engine 2 and from the coolant/recirculated exhaust gases exchanger. 

1. Device for thermal control of recirculated gases of an internal combustion engine, comprising a circuit of liquid coolant connected to an internal combustion engine, the circuit comprising first coolant/air heat exchanger means, arranged in a first loop connected to the engine, second coolant/recirculated exhaust gases heat exchanger means arranged in a second loop connected in parallel to the first loop to enable supplying the second heat exchanger means with coolant from the first heat exchanger means, wherein the ends of the second loop are directly connected to the body of the first heat exchanger means.
 2. Thermal control device according to claim 1, wherein the ends of the second loop are connected to an inlet and an outlet, respectively, of the first heat exchanger means distinct from the inlet and outlet connecting the first heat exchanger means to the engine.
 3. Thermal control device according to claim 1, wherein the ends of the second loop are connected to the first heat exchanger means so as to connect the inlet and outlet of the second heat exchanger means with an outlet and an inlet, respectively, of the first heat exchanger means.
 4. Thermal control device according to claim 1, wherein the first heat exchanger means comprise at least one heat exchanger core connected to a fluid inlet assembly and a fluid outlet assembly, and the ends of the second loop are directly connected to the fluid inlet and outlet assemblies, respectively.
 5. Thermal control device according to claim 1, wherein the second loop comprises controlled means for activating the coolant flow rate.
 6. Thermal control device according to claim 2, which comprises means for controlling the coolant flow rate allowed to circulate in the first loop.
 7. Thermal control device according to claim 6, wherein the means for controlling the flow rate comprise a valve of the proportional type.
 8. Thermal control device according to claim 6, wherein the means for controlling the flow rate comprise a pump.
 9. Thermal control device according to claim 6, wherein the second loop comprises controlled means for activating the coolant flow rate, and wherein the means for activating the flow rate in the second loop and the means for controlling the flow rate in the first loop are independent, so as to enable starting or stopping the means for activating the flow rate in the second loop whatever the flow rate of coolant allowed to circulate in the first loop.
 10. Thermal control device according to claim 1, wherein the first coolant/air heat exchanger means comprises a radiator.
 11. Thermal control device according to claim 5, wherein the means for activating the coolant flow rate is a pump.
 12. Thermal control device according to claim 7, wherein the valve of the proportional type is a thermostat. 